Two teenage rappers who carried out the “callous” killing of a drug dealer they wanted to rob and who was stabbed in the heart with a combat knife have been jailed.

Adam Chambers, 30, was attacked by 15-year-old Dval Doh after arranging to meet a customer at the back of a block of flats in Woolwich, south east London, on June 13.

Doh, now aged 16, was seen to be laughing as he walked away with Felou Abadja, 19, the Old Bailey heard.

Judge John Dodd QC told them: “The callous behaviour of both you throughout the events of that June day are breathtaking.”

He said Abadja had recruited and exploited Doh but the youngster, who had already been excluded from school for carrying a knife, had acted with “a degree of enthusiasm” in the events on the day of the killing.

The knife used was “a ghastly weapon” which had no place in a civil society, the judge said.

The judge described Abadja as appearing to him as someone who seemed to have “no sense of moral compass at all” and said he had shown “ruthlessness” in order to protect his position.

Doh, who had been given a referral order for carrying a knife into school, “knew full well despite the implications, the dangers of carrying a knife at the time” of going to rob Mr Chambers, the judge said.

The teenagers were cleared of murder at an Old Bailey trial but convicted of manslaughter and having a blade.

Doh, of Charlton, south east London, was sentenced to 12 years for manslaughter in a young offenders institution with an extended licence for four years.

He was also given a two-year sentence for having a blade in public and a five-day sentence for possession of class A drugs – both of which are to be served concurrently.

Abadja of Eltham, south London, was sentenced to 18 years for manslaughter with an extended licence for four years.

He was also given a three-year sentence for having a blade in public and a seven-day sentence for possession of cocaine – both to be served concurrently.

Prosecutor Sarah Whitehouse QC had told jurors how the defendants had been recording rap music at a studio in Blackheath, south east London, earlier on the day of the stabbing.

Just before 5pm, Abadja, known as TV, had called for a minicab to take him to Troughton Road, near to where he had arranged to meet Mr Chambers.

CCTV footage showed the victim arriving on his moped and then driving off 12 seconds later.

In that time, Doh had stabbed Mr Chambers, who made his escape on the moped but collapsed nearby.

Mrs Whitehouse told jurors: “Mr Abadja and (the youth) fled back to the minicab. They were talking and laughing but seemed in a hurry and said ‘let’s go boss’ to the driver.”

Mr Chambers suffered a wound 20cm deep and 7cm wide and was pronounced dead before 6.30pm that day.

Following his arrest at home in Eltham, Abadja admitted being at the scene and witnessing the victim fighting with the other boy but claimed he was metres away when the stabbing happened.

Doh was arrested days later and a large Predator combat knife – later found to be the murder weapon – and four wraps of heroin were seized from his bag.

Doh went on to admit having a blade in public and possession of class A drugs and Abadja pleaded guilty to having cocaine.

Mr Chambers’ father Steven Chambers said in a statement read in court: “These people who think it’s ok to take someone’s life need to be off our streets so that they cannot inflict this pain on another living soul.

“I spend every day thinking why, why Adam?”

Mr Chambers was in the situation he was in because he was trying to earn money to pay rent arrears, according to his mother Jacqui Edmonds.

She described her son as a much-loved father to a six-year old daughter, and a nephew, uncle and friend.

She said: “I will never get over losing him. I know my family never will.”